MBOTC Terms
bi-orientation
The attachment of sister chromatids to opposite poles of the mitotic spindle, so that they move to opposite ends of the cell when they separate in anaphase.
bivalent
A four-chromatid structure formed during meiosis, consisting of a duplicated chromosome tightly paired with its homologous duplicated chromosome.
ABC transporters
A large family of membrane transport proteins that use the energy of ATP hydrolysis to transfer peptides or small molecules across membranes.
Bak
A main effector Bcl2 family protein of the intrinsic pathway of apoptosis in mammalian cells that is bound to the mitochondrial outer membrane even in the absence of an apoptotic signal; activation is usually by activated pro-apoptotic BH3-only proteins.
Bax
A main effector Bcl2 family protein of the intrinsic pathway of apoptosis in mammalian cells; located mainly in the cytosol and translocates to the mitochondria only after activation, usually by activated pro-apoptotic BH3-only proteins.
antigen
A molecule that can induce an adaptive immune response or that can bind to an antibody or T cell receptor
AIRE (autoimmune regulator)
A protein expressed by a subpopulation of epithelial cells in the thymus that stimulates the production of small amounts of self proteins characteristic of other organs, exposing developing thymocytes to these proteins for the purpose of self-tolerance.
allosteric protein
A protein that can adopt at least two distinct conformations, and for which the binding of a ligand at one site causes a conformational change that alters the activity of the protein at a second site; this allows one type of molecule in a cell to alter the fate of a molecule of another type, a feature widely exploited in enzyme regulation.
acid
A proton donor. Substance that releases protons (H+) when dissolved in water, forming hydronium ions (H3O+) and lowering the pH
base
A substance that can reduce the number of protons in solution, either by accepting H+ ions directly, or by releasing OH- ions, which then combine with H+ to form H2O.
antigenic variation
Ability to change the antigens displayed on the cell surface; a property of some pathogenic microorganisms that enables them to evade attack by the adaptive immune system.
antibody response
Adaptive immune response in which B cells are activated to secrete antibodies that circulate in the bloodstream or enter other body fluids, where they can bind specifically to the foreign antigen that stimulated their production.
Apaf1
Adaptor protein of the intrinsic apoptotic pathway; on binding cytochrome c, oligomerizes to form an apoptosome.
adhesion belt
Adherens junctions in epithelia that form a continuous belt (zonula adherens) just beneath the apical face of the epithelium, encircling each of the interacting cells in the sheet.
Bcl2
Anti-apoptotic Bcl2 family protein of the outer mitochondrial membrane that binds and inhibits pro-apoptotic Bcl2 family proteins and prevents inappropriate activation of the intrinsic pathway of apoptosis.
BclXL
Anti-apoptotic Bcl2 family protein of the outer mitochondrial membrane that binds and inhibits pro-apoptotic Bcl2 family proteins and prevents inappropriate activation of the intrinsic pathway of apoptosis.
axoneme
Bundle of microtubules and associated proteins that forms the core of a cilium or a flagellum in eukaryotic cells and is responsible for their movements.
antiporter
Carrier protein that transports two different ions or small molecules across a membrane in opposite directions, either simultaneously or in sequence.
asymmetric cell division
Cell division in which some important molecule or molecules are distributed unequally between the two daughter cells, causing these cells to become different from each other.
adherens junction
Cell junction in which the cytoplasmic face of the plasma membrane is attached to actin filaments. Examples include adhesion belts linking adjacent epithelial cells and focal contacts on the lower surface of cultured fibroblasts.
anchoring junction
Cell junction that attaches cells to neighboring cells or to the extracellular matrix.
antigen-presenting cell
Cell that displays foreign antigen complexed with an MHC protein on its surface for presentation to T lymphocytes.
allostery
Change in a protein's conformation brought about by the binding of a regulatory ligand (at a site other than the protein's catalytic site), or by covalent modification. The change in conformation alters the activity of the protein and can form the basis of directed movement
aquaporin (water channel)
Channel protein embedded in the plasma membrane that greatly increases the cell's permeability to water, allowing transport of water, but not ions, at a high rate across the membrane.
bacterial artificial chromosome (BAC)
Cloning vector that can accommodate large pieces of DNA, typically up to 1 million base pairs.
alpha helix
Common folding pattern in proteins, in which a linear sequence of amino acids folds into a righthanded helix stabilized by internal hydrogen-bonding between backbone atoms.
beta sheet (β sheet)
Common structural motif in proteins in which different sections of the polypeptide chain run alongside each other, joined together by hydrogen-bonding between atoms of the polypeptide backbone. Also known as a β pleated sheet
ARP (actin-related protein) complex (Arp 2/3 complex)
Complex of proteins that nucleates actin filament growth from the minus end.
base excision repair
DNA repair pathway in which single faulty bases are removed from the DNA helix and replaced.
anchorage dependence
Dependence of cell growth, proliferation, and survival on attachment to a substratum.
antiparallel
Describes the relative orientation of the two strands in a DNA double helix or two paired regions of a polypeptide chain; the polarity of one strand is opposite to that of the other.
autophagy
Digestion of cytoplasm and worn-out organelles by the cell's own lysosomes.
BiP
Endoplasmic reticulum (ER)-resident chaperone protein member of the family of hsp70-type chaperone proteins.
aminoacyl-tRNA synthetase
Enzyme that attaches the correct amino acid to a tRNA molecule to form an aminoacyl-tRNA
Bcl2 family
Family of intracellular proteins that either promote or inhibit apoptosis by regulating the release of cytochrome c and other mitochondrial proteins from the intermembrane space into the cytosol.
apoptosis
Form of programmed cell death, in which a "suicide" program is activated within an animal cell, leading to rapid cell death mediated by intracellular proteolytic enzymes called caspases.
AMPA receptor
Glutamate-gated ion channel in the mammalian central nervous system that carries most of the depolarizing current responsible for excitatory postsynaptic potentials.
angiogenesis
Growth of new blood vessels by sprouting from existing ones.
amphiphilic
Having both hydrophobic and hydrophilic regions, as in a phospholipid or a detergent molecule.
apoptosome
Heptamer of Apaf1 proteins that forms on activation of the intrinsic apoptotic pathway; it recruits and activates initiator caspases that subsequently activate downstream executioner caspases to induce apoptosis.
acid hydrolases
Hydrolytic enzymes—including proteases, nucleases, glycosidases, lipases, phospholipases, phosphatases, and sulfatases—that work best at acidic pH; these enzymes are found within the lysosome
astral microtubule
In the mitotic spindle, any of the microtubules radiating from the aster which are not attached to a kinetochore of a chromosome.
acetyl CoA
Small water-soluble activated carrier molecule. Consists of an acetyl group linked to coenzyme A (CoA) by an easily hydrolyzable thioester bond.
axon
Long nerve cell projection that can rapidly conduct nerve impulses over long distances so as to deliver signals to other cells.
arrestin
Member of a family of proteins that contributes to GPCR desensitization by preventing the activated receptor from interacting with G proteins and serving as an adaptor to couple the receptor to clathrin-dependent endocytosis.
bacterium (plural bacteria) (eubacterium)
Member of the domain bacteria, one of the three main branches of the tree of life (archaea, bacteria, and eukaryotes). Bacteria and archaea both lack a distinct nuclear compartment, and together comprise the prokaryotes.
acetylcholine receptor (AChR)
Membrane protein that responds to binding of acetylcholine (ACh). The nicotinic AChR is a transmitter-gated ion channel that opens in response to ACh. The muscarinic AChR is not an ion channel, but a G-protein-coupled cell-surface receptor.
adenylyl cyclase
Membrane-bound enzyme that catalyzes the formation of cyclic AMP from ATP. An important component of some intracellular signaling pathways.
activated carrier
Small diffusible molecule that stores easily exchangeable energy in the form of one or more energy-rich covalent bonds. Examples are ATP, acetyl CoA, FADH2, NADH, and NADPH.
ARF proteins
Monomeric GTPase in the Ras superfamily responsible for regulating both COPI coat assembly and clathrin coat assembly
active transport
Movement of a molecule across a membrane or other barrier driven by energy other than that stored in the electrochemical or concentration gradient of the transported molecule
beta-catenin (β-catenin)
Multifunctional cytoplasmic protein involved in cadherin-mediated cell-cell adhesion, linking cadherins to the actin cytoskeleton. Can also act independently as a transcription regulatory protein. Has an important role in animal development as part of a Wnt signaling pathway
ATP (adenosine 5′-triphosphate)
Nucleoside triphosphate composed of adenine, ribose, and three phosphate groups. The principal carrier of chemical energy in cells. The terminal phosphate groups are highly reactive in the sense that their hydrolysis, or transfer to another molecule, takes place with the release of a large amount of free energy
ADP (adenosine 5′-diphosphate)
Nucleotide produced by hydrolysis of the terminal phosphate of ATP. Regenerates ATP when phosphorylated by an energy-generating process such as oxidative phosphorylation
benign
Of tumors: self-limiting in growth, and noninvasive.
allele
One of several alternative forms of a gene. In a diploid cell, each gene will typically have two alleles, occupying the corresponding position (locus) on homologous chromosomes
Antennapedia complex
One of two gene clusters in Drosophila that contain Hox genes; genes in the Antennapedia complex control the differences among the thoracic and head segments of the body.
Bithorax complex
One of two gene clusters in Drosophila that contain Hox genes; genes in the Bithorax complex control the differences among the abdominal and thoracic segments of the body.
autophagosome
Organelle surrounded by a double membrane contains engulfed cytoplasmic cargo in the initial stages of autophagy
amino acid
Organic molecule containing both an amino group and a carboxyl group. Those that serve as building blocks of proteins are alpha amino acids, having both the amino and carboxyl groups linked to the same carbon atom.
antenna complex
Part of a photosystem that captures light energy and channels it into the photochemical reaction center. It consists of protein complexes that bind large numbers of chlorophyll molecules and other pigments.
autoimmune disease
Pathological state in which the body mounts a disabling adaptive immune response against one or more of its own molecules
bacteriorhodopsin
Pigmented protein found in the plasma membrane of a salt-loving archaeon, Halobacterium salinarium (Halobacterium halobium). Pumps protons out of the cell in response to light
auxin
Plant hormone, commonly indole-3-acetic acid, with numerous roles in plant growth and development.
aerobic respiration
Process by which a cell obtains energy from sugars or other organic molecules by allowing their carbon and hydrogen atoms to combine with the oxygen in air to produce CO2 and H2O, respectively.
anti-IAP
Produced in response to various apoptotic stimuli and, by binding to IAPs and preventing their binding to a caspase, neutralize the inhibition of apoptosis provided by IAPs.
alternative RNA splicing
Production of different RNAs from the same gene by splicing the transcript in different ways.
affinity maturation
Progressive increase in the affinity of antibodies for the immunizing antigen with the passage of time after immunization.
ATR (ataxia telangiectasia and Rad3 related protein)
Protein kinase activated by DNA damage. If damage remains unrepaired, ATR helps initiate a signal cascade that culminates in cell cycle arrest. Related to ATM.
ATM (ataxia telangiectasia mutated protein)
Protein kinase activated by double-strand DNA breaks. If breaks are not repaired, ATM initiates a signal cascade that culminates in cell cycle arrest. Related to ATR.
antibody
Protein secreted by activated B cells in response to a pathogen or foreign molecule. Binds tightly to the pathogen or foreign molecule, inactivating it or marking it for destruction by phagocytosis or complement-induced lysis.
anti-apoptotic Bcl2 family proteins
Proteins (e.g., Bcl2, BclXL) on the cytosolic surface of the outer mitochondrial membrane that bind and inhibit pro-apoptotic Bcl2 family proteins and thereby help prevent inappropriate activation of the intrinsic pathway of apoptosis
action potential
Rapid, transient, self-propagating electrical excitation in the plasma membrane of a cell such as a neuron or muscle cell. Action potentials, or nerve impulses, make possible long-distance signaling in the nervous system.
apical
Referring to the tip of a cell, a structure, or an organ. The apical surface of an epithelial cell is the exposed free surface, opposite to the basal surface. The basal surface rests on the basal lamina that separates the epithelium from other tissue.
active site
Region of an enzyme surface to which a substrate molecule binds in order to undergo a catalyzed reaction.
binding site
Region on the surface of one molecule (usually a protein or nucleic acid) that can interact with another molecule through noncovalent bonding.
amyloid fibrils
Self-propagating, stable β-sheet aggregates built from hundreds of identical polypeptide chains that become layered one over the other to create a continuous stack of β sheets. The unbranched fibrous structure can contribute to human diseases when not controlled.
anticodon
Sequence of three nucleotides in a transfer RNA (tRNA) molecule that is complementary to a three-nucleotide codon in a messenger RNA (mRNA) molecule.
Akt
Serine/threonine protein kinase that acts in the PI-3- kinase/Akt intracellular signaling pathway involved especially in signaling cells to grow and survive. Also called protein kinase B (PKB).
Agrin
Signal protein released by an axonal growth cone during formation of the synapse between it and a muscle cell.
archaeon (plural arch[a]ea) (archaebacterium)
Singlecelled organism without a nucleus, superficially similar to bacteria. At a molecular level, more closely related to eukaryotes in genetic machinery than are bacteria. Archaea and bacteria together make up the prokaryotes
basal
Situated near the base. Opposite the apical surface
adhesins
Specific proteins or protein complexes of pathogenic bacteria that recognize and bind cell-surface molecules on the host cells to enable tight adhesion and colonization of tissues.
antigenic determinant
Specific region of an antigen that binds to an antibody or a complementary receptor on the surface of a B cell (BCR) or T cell (TCR).
anaphase A
Stage of mitosis during which chromosome segregation occurs as chromosomes move toward the two spindle poles.
anaphase B
Stage of mitosis during which chromosome segregation occurs as spindle poles separate and move apart.
anaphase
Stage of mitosis during which sister chromatids separate and move away from each other. (2) Anaphase I and II: stages of meiosis during which chromosome homolog pairs separate (I), and then sister chromatids separate
antibiotic
Substance such as penicillin or streptomycin that is toxic to microorganisms. Often a natural product of a particular microorganism or plant.
adaptive immune system
System of lymphocytes providing highly specific and long-lasting defense against pathogens in vertebrates. It consists of two major classes of lymphocytes: B lymphocytes (B cells), which secrete antibodies that bind specifically to the pathogen or its products, and T lymphocytes (T cells), which can either directly kill cells infected with the pathogen or produce secreted or cell-surface signal proteins that stimulate other host cells to help eliminate the pathogen.
activation-induced deaminase (AID)
The enzyme catalyzing the processes of somatic hypermutation and immunoglobulin class switching in activated B cells.
activation energy
The extra energy that must be acquired by atoms or molecules in addition to their ground-state energy in order to reach the transition state required for them to undergo a particular chemical reaction
BH3-only proteins
The largest subclass of Bcl2 family proteins. Produced or activated in response to an apoptotic stimulus and promote apoptosis mainly by inhibiting antiapoptotic Bcl2 family proteins.
B cell receptor (BCR)
The transmembrane immunoglobulin protein on the surface of a B cell that serves as its receptor for antigen.
basement membrane
Thin mat of extracellular matrix that separates epithelial sheets, and many other types of cells such as muscle or fat cells, from connective tissue. Also called basal lamina
basal lamina (plural basal laminae)
Thin mat of extracellular matrix that separates epithelial sheets, and many other types of cells such as muscle or fat cells, from connective tissue. Sometimes called basement membrane.
ATP synthase (F1Fo ATPase)
Transmembrane enzyme complex in the inner membrane of mitochondria and the thylakoid membrane of chloroplasts. Catalyzes the formation of ATP from ADP and inorganic phosphate during oxidative phosphorylation and photosynthesis, respectively. Also present in the plasma membrane of bacteria
base pair
Two nucleotides in an RNA or DNA molecule that are held together by hydrogen bonds—for example, G paired with C, and A paired with T or U.
anaphase-promoting complex
Ubiquitin ligase that catalyzes the ubiquitylation and destruction of securin and M- and S-cyclins, initiating the separation of sister chromatids in the metaphase-to-anaphase transition during mitosis.
General term for a protein that functions solely to link two or more different proteins together in an intracellular signaling pathway or protein complex.
adaptor protein
adaptation
adjustment of sensitivity following repeated stimulation. The mechanism that allows a cell to react to small changes in stimuli even against a high background level of stimulation.